1. Field of the Disclosure
The present disclosure relates in general to patient monitoring and in particular to oximeter patient monitors capable of indicating probe off conditions.
2. Description of the Related Art
Oximeter systems providing measurements of a monitored patient have become the standard of care in many patient care settings, including surgical, post surgical, neonatal, general ward, home care, physical training, and the like. In general, oximeter systems accept one or more noninvasive signals from an optical sensor or probe capable of emitting light into a tissue site and capable of detecting light attenuated by the tissue site. Accurate determination of the measurements and audio/visual indications is often dependent upon proper application of the optical sensor to the tissue site. In the present disclosure, “probe on” conditions include their ordinary broad meaning known to one of skill in the art, including designating proper application of an optical probe to a measurement site. “Probe off” conditions include their ordinary broad meaning known to one of skill in the art, including designating improper application of an optical probe to a measurement site.
Many oximeters may fail to accurately detect probe off conditions. As stated, this condition occurs when the optical sensor becomes partially or completely dislodged from the patient (measurement site), but continues to detect signals. Probe off errors can be serious because the oximeter may output normal measurements, and audio/visual indications of the monitored parameters when, in fact, the probe is not properly attached to the patient, probe off errors may potentially lead to missed physiological events.
Several solutions to more accurately monitor and detect probe off conditions are disclosed in U.S. Pat. No. 6,654,624, assigned to Masimo Corporation (“Masimo”) of Irvine, Calif., and incorporated by reference herein. For example, the '624 patent discloses monitor-based detection of probe off conditions. In particular, an intelligent, rule-based processor uses signal quality measurements to limit the operating region of the oximeter without significant negative impact on low perfusion performance. These signal-quality operating limits are superimposed on a graph of signal strength versus emitter gain to improve probe off detection. In this manner, the oximeter can reject intensity signals that have sufficient signal strength to fall within an operating region, but that are unlikely to be a plethysmograph signal. One signal quality measurement that is used is pulse rate density, which is the percentage of time detected pulses satisfy a physiologically acceptable model. Another signal quality measurement is harmonic energy ratio, which is the percentage of signal energy that occurs at the pulse rate and its harmonics. The operating region of the oximeter is then defined in terms of signal strength versus gain, signal strength versus PR density and energy ratio versus predefined energy ratio limits. Thus, the '624 disclosure seeks to limit the scope of acceptable probe on space, as defined by signal strength versus gain, PR density, and energy ratios, and seeks to designate all non-probe on space as probe off space.